Skills associated with literacy and numeracy carry important implications for consumers. However, past research on illiterate consumers is almost non-existent. In this study, a variety of methods, such as in-depth interviews and observations in a shopping environment, were used to understand consumer illiteracy and innumeracy. The sample consisted of students at an adult education center. Themes from in-depth interviews of students and teachers suggest a high degree of concrete thinking exemplified by dependence on audio-visual information, short-term orientation, use of numbers as concrete information, intuitive processing, and an emphasis on contextual learning. Related themes include dependence on others and maintenance of self-esteem in service encounters. Behavioral outcomes observed include perceptual decision-making, and high loyalty to retail outlets. These themes were more accentuated at lower levels of literacy, where extreme dependence on others and the use of rudimentary defensive practices to avoid negative experiences were common. Observations from classroom activities and tutoring and from shopping trips reinforced existence of these themes and suggested a model of decision-making with little effort spent on evaluation of alternatives. From an information processing perspective, most of the effort is spent on perceptual processes such as locating a product and determining price information. This research raises fundamental theoretical issues relating to the adequacy of existing models of consumer behavior in capturing decision-making of illiterate consumers, as well as important practical implications for marketers.